The Middle Ages

A Medieval History Asylum

Dec. 6th, 2016

The Cambrian Explosion: The Environmental Context of Ediacarian and Cambrian Events, part 2

mood: awake

The next few chapters won't be particularly well-organized -- no time sequence, no easy logical reason to progress from one topic to another.

A brief summary of the carbon cycle, and the Snowball Earth hypothesis

First, the carbon cycle

This becomes necessary for understanding a bunch of evidence and just how life affects its environment.

Carbon, an element, is for the most part neither created or destroyed on Earth; it just goes into a bunch of different configurations and different places. The majority of the Earth's carbon isn't inside living things or in the oceans or atmosphere, but locked up in rocks and in the magma in the Earth's mantle. It can also be in the atmosphere, as carbon dioxide. As just about everyone who's not lost in global warming denial now knows, carbon dioxide in the atmosphere has a "greenhouse effect", trapping the sun's energy and warming the planet.

If adding infill development to suburban neighborhoods is untenable (and it absolutely is in most jurisdictions) then consciously devolving back to a rural framework is the better option, particularly as property values drop and populations contract. The goal is to get local tax revenues in line with the cost of local critical infrastructure and municipal services. . . .

And the article offers multiple examples like that.

If the municipal water supply becomes too expensive to maintain it might be time to consider snipping the umbilical cord and switching to individual private wells or rainwater catchment systems. No? That seems ridiculous? Okay. Wait. Let an insolvent system defer upkeep and cut corners for a few decades. Flint, Michigan did that. What could go wrong?

Nov. 27th, 2016

The Cambrian Explosion: The Environmental Context of Ediacarian and Cambrian Events, part one

mood: awake

music: Jupiter, Bringer of Jollity

(I am skipping over the chapter "The Geological Context of Ediacaran and Cambrian Events", because what I'd like to cover from there can easily be rolled up into this chapter.)

Some of the most dramatic environmental changes of the past 2 billion years occurred during late Neoproterozoic and early Cambrian times. The late Neoproterozoic world was, quite literally, a different Earth: atmospheric oxygen levels were much lower than today, and the deep oceans were oxygen poor but iron rich, perhaps similar to the noxious brew deep in the present Black Sea.

That's a damn good opening paragraph and I'm sticking with it. The rest of the chapter is how we know that, and how it changed; it wasn't a steady progression, and some of the evidence is so bizarre, we're not really sure what was going on. Suffice it to say, Earth in the last hundred million years before the Cambrian Period was a weird, weird, place!

Nov. 26th, 2016

The Cambrian Explosion: first, some scattered notes

mood: awake

The time period covered by The Cambrian Explosion runs from approximately 635 million years ago to 485 million years ago, which covers two formally recognized periods in Earth's prehistory, the Ediacaran Period and the Cambrian Period. This stretch of time is when almost all the phyla of animals now living first evolved, and it's the famous time when evolution went into nitro-fuel mode, running so fast that creationists claim it couldn't possibly be natural.

Some of the following stuff is from the book, and some of it isn't.

Back some years ago, a scientist named Paul Hoffman made a dramatic claim: far in the Earth's past, before life was more than single-celled critters, the whole damn Earth froze over from pole to pole in a gigantic glaciation that made the Pleistocene ice ages look tropical. He called this the "Snowball Earth" hypothesis. Like an increasing number of scientists, Hoffman is very good at taking his case to the media, but other scientists don't all agree with him about just how frozen Earth really was, and how many times this happened. There may have been areas of open ocean. In any case, there would still have been deep-sea thermal vents where life could have survived. The one thing everybody agrees upon is that the Earth did indeed suffer through several colossal ice ages, and most of it, if not quite all of it, was very cold. What life there was back then must have had a tough time just surviving. We've even got a decent idea of when each of these monster ice ages happened.

At any rate, the Ediacaran Period starts just as the last really huge glaciation, the Marinoan, ends, 635 million years ago. There was one more ice age, the Gaskiers glaciation, between 514 and 513 million years ago, but it was milder and less extensive than the full Snowball Earth ones. After that, Snowball Earth conditions ended for good, and life started enjoying some good weather for a change.

The beginning of the next period, the Cambrian Period, has been moved earlier than it used to be. Thus, a lot of rather interesting things that happened back then are now considered to have happened in the early Cambrian instead of the Ediacaran. Back in Darwin's day, and through much of the twentieth century, the start of the Cambrian used to be when the first fossils of any life at all appeared. In fact, that was one of the major challenges to Darwin's theory: how can you say life evolved, when it seems to just poof into existence at this point? Poor Darwin worried quite a bit about it, but thought we might eventually find earlier fossils.

He was right. We have, and you're going to read a lot about them (if I keep writing this). But throughout the Ediacaran and much (not all) of the Cambrian Period, there was no land life -- except maybe microbes living in a microbial crust in some places. The land was just bare rock and basins full of gravel and boulders, though it would have had freshwater streams running across it and emptying into the oceans. No land plants, and certainly no land animals. All multicellular life lived in the oceans. Think about that.

Geologists have declared that the Cambrian Period officially starts with the appearance of a fossil called Treptichnus pedum. That's not actually an animal, but the fossil trace of the animal -- its burrow, we think. Since we never find any bits of carapace or skeleton in the burrows, presumably it didn't have any hard parts. For what it's worth, priapulid worms create burrows with a similar shape.

Timeline suggested by the book:

-- Life probably began around 3.5 billion years ago.

-- The earliest eukaryotes (critters either one-celled or multicellular who all have their DNA nicely contained in a nucleus instead of floating around freely in their protoplasm) show up by 1.8 billion years ago.

-- First fossils that everybody agrees are of multicellular life, algae, appear 1.2 billion years ago.

-- Supercontinent Rodinia forms before one billion years ago.

-- It starts to break up around the time of the Sturtian glaciation, 717 million years ago.

-- By Ediacaran time (around 635 million years ago), it's no longer a supercontinent but a series of scattered continents, and oxygen levels are starting to rise.

-- During the first part of the Cambrian Period, called either Stage 1 or the Fortunian, you see some wee tubes, cones, spicules, "shells", and other stuff appear. They get more and more diverse as time goes on; multicellular life is now taking hold and getting complex. These are the "small shelly fauna" (SSF); pay attention to that phrase, because it'll pop up again. We also see more worm tubes and other trace fossils. Also, an odd group of sponges, the archaeocyathids, show up and start diversifying; they've got a decent fossil record because they have calcium skeletons that preserve fairly well.

-- At the beginning of Stage 3, we see the earliest trilobite fossils yet found, but the book doesn't name a genus. Maybe it was just bits of the exoskeleton? You also see more traces of burrowing in the sea floor, as bigger worms and other critters evolved. The Chengjiang fauna of China dates back to this time; it's solid evidence the famous Cambrian explosion was already underway. By now, the world has changed from the Ediacaran: there's much more oxygen in the atmosphere, and the once-smooth microbial mat on the sea floor no longer exists because the burrowers have eaten it into extinction.

-- Stage 4 starts with the appearance of either Ollenellus or Redlichia, two trilobite genera.

-- No formal definitions of the beginning for the remaining stages of the Cambrian Period, alas.

Nov. 25th, 2016

Election Recount

DONATE & FORWARD! 2 states are covered and they are partway on the 3rd. EVERYONE should care about this. Even trump said he didn't trust the system and wouldn't accept the results... until it worked in his favour. Americans deserve to know if anomolies in such a close election are just that, anomolies, or if the system is broken (hacked etc) and needs fixing. (IMHO every election that is close or goes unexpectedly should automatically trigger a recount in relevant states w/o having to sue for it.)